Has it been a success? Before I answer that question by citing the law of unintended consequences, I have to concede that the change was a necessity. MPs had faffed around the question for 25 years, since a trial period for TV was recommended under the newly elected Labour government in 1964. It was ignored. So was a brief experiment – just three days – in the Lords in 1968. Radio microphones were allowed into the Commons on 3 April 1978 (Welsh question time; I was present), which traditionalists deemed bad enough. It would encourage exhibitionists (as if they weren't already encouraged) and the trivialisation of politics, they said. Another vote on TV was narrowly defeated, though the unelected Lords – people who don't face the voters and feel they deserve more attention – went modern when TV transmissions began on 23 January 1985.

What happened? That old showman, Harold Macmillan, the first prime minister (1957-63) to handle TV like a pro ("Between these four walls …" he once confided to a camera), stole the show by using the new platform to attack Margaret Thatcher's economic policies. The Commons dithered on for four more years.

Most parliamentary exchange is much duller, and so it should be. We cannot have our politicians high on adrenalin all the time. But the electorate sat through the Iraq war debate and revolt in March 2003 – American voters were impressed by the eloquence and vitality compared to windbaggery in Congress. Fox hunting, gay rights, the right to die – social issues have usually filled the chamber rather than the "whither Europe?" or "what price Hong Kong?" debates of yesteryear. In 2009, MPs have been shown painfully wanting as they grappled with their own shortsighted folly over their allowances and expenses.

There have been good developments. The sight of so many white middle-aged men added a spur to pressures to make parliament more diverse to reflect the realities of modern urban Britain: more women, more black and Asian MPs, even a disabled one – though fewer and fewer white working class.

Yet the paradox of 20 years of TV is that the Commons has been much diminished in the process. It is not all telly's fault. New Labour introduced more "family-friendly hours" and Tony Blair ignored parliament when he could, as does Gordon Brown. There has been no major big set-piece debate worthy of the name on an issue like Iraq for years. Brown simply does not do them.

TV is part of that calculation. It raises the stakes in ways that old-fashioned informality did not. How can you be civil to an opponent if voters fail to understand on TV? Soundbite abuse works better for telly, as it does in Big Brother and the Sun, but it coarsens the tone of public debate. Sorry about that.

The most damning inintended consequence was not predicted, not that I recall. By putting an in-house parliamentary feed into every peer and MP's office room, every official and press reporter's too, it allows us all in the Westminster village to keep an eye on the chamber – actually, both chambers – while getting on with our "real" work such as reading, talking and emailing. So when voters ask "where are all the MPs?" as they watch the empty green leather benches, the answer is "watching it on TV, the same as you". Ditto the press gallery, usually as empty as the chamber except at PMQs.

It may be that a great Victorian debating chamber is no longer the best place in which to hold ministers to account on behalf of voters. I'm not convinced. On major issues it remains the best way – gladiatorial combat which puts a politician on his/her mettle so all can see.